Metal-organic (MO) precursor vapor is commonly used for the thermal deposition of metal films inside a well-controlled processing chamber. Metal-organic precursors are usually in liquid or solid form. Metal-organic vapor is usually generated thermally inside a closed vessel or ampoule. Molecules of the MO precursor are then delivered to a wafer surface inside the processing chamber through a delivery gasline. In order to prevent the vapor reverting back to its bulk form, the delivery gasline is usually thermally controlled to be well above the dew point of the particular MO precursor.
In order to have efficient delivery, an inert gas is usually used to carry the precursor vapor along the delivery line. The purpose of this carrier gas is mainly two-fold: (1) to increase the vapor pressure of the precursor due to agitation of gas flow into the vessel; and (2) to dilute the precursor inside the delivery line to raise the thermal decomposition temperature of the precursor.
After the deposition process reaches a predetermined thickness, an ampoule outlet pneumatic valve is closed; leaving the delivery line with a substantial amount of unused precursor vapor. This unused vapor should be quickly removed to preserve the well-controlled process performance. If not removed quickly, the residual precursor can accumulate to form various particulates which may contaminate the deposited film.
Most metal-organic chemical vapor deposition (MOCVD) processes of metal films are deposited using synthesized metastable chemicals as the precursors. Some of metal-organic precursors decompose readily at very low temperature. In order to achieve well-controlled process performance—such as precise thickness and low particle contamination—management of the residual precursor vapor in the delivery line post-deposition can be important. If the residual precursor is not removed promptly, it will be added to the subsequent deposition process. The residue can accumulate to form particles, which will be pushed onto wafer surface. Therefore, there is a need in the art for apparatus and methods to provide improved removal of residual precursor.